Capacitive sensor devices, which can be, for example, arranged at a hand-held device in order to detect a gripping of the hand-held device with one hand are known from prior art. A change of the dielectric properties in the area of the sensor electrodes of the capacitive sensor device suggests a gripping of the hand-held device with one hand. When a gripping of the hand-held device with one hand is detected, the hand-held device can be, for example, switched from a sleep mode to an active mode.
With the capacitive sensor devices for the detection of a gripping of a hand-held device with one hand known from prior art, the problem is that, depending on the technology used, the gripping of the hand-held device with one hand cannot be reliably detected in case of good or poor ground reference.
Prior art has tried to solve this problem in such a way that a switching of the supply voltage of an electrical hand-held device is detected, wherein an alternative measuring mode is activated when a switching of the supply voltage is detected, which also enables the detection of a gripping of the hand-held device in case of good ground reference. For example, an electrical hand-held device is well grounded when the ground reference of the device is, for example, effected via a connected USB cable. In addition to the data transmission, the USB connector also provides a voltage of 5 V for the power supply of USB devices, which can be detected in order to take corresponding measures with respect to the measuring mode.
This way, it can be determined that the device providing the power supply for the hand-held device has a good ground reference. However, it cannot be determined how good the ground reference is actually. A further disadvantage is that the ground reference can also be modified in a different way. For example, touching a part of an electrical hand-held device being connected to ground, can lead to a stronger coupling to ground. Such a modification of the ground reference may not be detected by the detection of the change of the supply voltage, since the supply voltage does not change.
On the other hand, devices with a fairly poor ground reference, such as a USB battery, can provide an alternative supply voltage. However, the modified supply voltage can be detected, but the alternative measuring mode described before will probably not be activated, since the ground reference changes only slightly or does not change at all with modified supply voltage. However, if the alternative measuring mode would still be used for the detection of a gripping of the hand-held device, the capacitive sensor device would no longer be able to reliably detect the gripping of a hand-held device without additional measures.
Furthermore, this way it is not possible to determine the actual ground reference.